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Event Handler that creates adds another event handler

 
 
kaczmar2@gmail.com
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      02-22-2007
I have an ASP.NET page where controls are created dynamically, and I
have an issue where one event handler creates another set of controls,
and then adds event handlers to those controls. The problem comes in
where I need to raise the event in the second control - the event does
not fire. I have distilled the example below down to it simplest:

on Page_Load one button is created, and a Click event hander is added
to the button. When this first button is clicked, it adds another
button and adds another onclick event for this new button.

The first time through, everything works - The first button is
clicked, and then the second button is added with its event handler.
The problem comes on this second postback - the Page_Load event fires,
but not the first button's event - the one the creates the second
button and EventHandler.

How can I get around this? How can I add controls and event handlers
from an event hander? Code is below:

<%@ Page Language="C#" %>

<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
Button button1 = new Button();
button1.ID = "button1";
button1.Text = "Button 1";
button1.Click += new EventHandler(button1_Click);
main.Controls.Add(button1); // main is the div
}

void button1_Click(object sender, EventArgs e)
{
Button button2 = new Button();
button2.ID = "button2";
button2.Text = "Button 2";
button2.Click += new EventHandler(button2_Click);
main.Controls.Add(button2); // main is the div
}

void button2_Click(object sender, EventArgs e)
{
// this event handler is never hit.
}

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>EventHandler Test</title>
</head>
<body>
<form id="form1" runat="server">
<div id="main" runat="server"></div>
</form>
</body>
</html>

 
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Damien
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Posts: n/a
 
      02-22-2007
On Feb 22, 2:00 am, (E-Mail Removed) wrote:
> I have an ASP.NET page where controls are created dynamically, and I
> have an issue where one event handler creates another set of controls,
> and then adds event handlers to those controls. The problem comes in
> where I need to raise the event in the second control - the event does
> not fire. I have distilled the example below down to it simplest:
>
> on Page_Load one button is created, and a Click event hander is added
> to the button. When this first button is clicked, it adds another
> button and adds another onclick event for this new button.
>
> The first time through, everything works - The first button is
> clicked, and then the second button is added with its event handler.
> The problem comes on this second postback - the Page_Load event fires,
> but not the first button's event - the one the creates the second
> button and EventHandler.
>
> How can I get around this? How can I add controls and event handlers
> from an event hander? Code is below:
>
> <%@ Page Language="C#" %>
>
> <script runat="server">
> protected void Page_Load(object sender, EventArgs e)
> {
> Button button1 = new Button();
> button1.ID = "button1";
> button1.Text = "Button 1";
> button1.Click += new EventHandler(button1_Click);
> main.Controls.Add(button1); // main is the div
> }
>
> void button1_Click(object sender, EventArgs e)
> {
> Button button2 = new Button();
> button2.ID = "button2";
> button2.Text = "Button 2";
> button2.Click += new EventHandler(button2_Click);
> main.Controls.Add(button2); // main is the div
> }
>
> void button2_Click(object sender, EventArgs e)
> {
> // this event handler is never hit.
> }
>
> </script>
>
> <html xmlns="http://www.w3.org/1999/xhtml" >
> <head runat="server">
> <title>EventHandler Test</title>
> </head>
> <body>
> <form id="form1" runat="server">
> <div id="main" runat="server"></div>
> </form>
> </body>
> </html>


Hi,

As you correctly pointed out, the problem is that during the second
postback, the additional button/event handlers are not added to the
page, so no event handlers fire.

If you have a small number of states through which your page can
transition, I'd recommend enumerating those, and tracking which state
your page is in using the viewstate. Then define a routine that
creates appropriate controls based on which state you're in. Then your
button clicks become:

state = newState;
BuildPageControls();

and you also call BuildPageControls during any postback (so it'll need
to be callable multiple times during a single postback, and not end up
creating duplicate controls)

That's one approach, if you've got a small number of states. If you've
got more complex logic, you may end up having to put more into your
viewstate to allow you to safely reconstruct the page.

Finally, does Button 1 have to add the new Button 2? Could it not just
exist on the page but be disabled?

Damien

 
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